CA1243493A - Steam-injected free-turbine-type gas turbine - Google Patents
Steam-injected free-turbine-type gas turbineInfo
- Publication number
- CA1243493A CA1243493A CA000473757A CA473757A CA1243493A CA 1243493 A CA1243493 A CA 1243493A CA 000473757 A CA000473757 A CA 000473757A CA 473757 A CA473757 A CA 473757A CA 1243493 A CA1243493 A CA 1243493A
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- CA
- Canada
- Prior art keywords
- turbine
- compressor
- steam
- core
- power
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000008878 coupling Effects 0.000 claims abstract description 8
- 238000010168 coupling process Methods 0.000 claims abstract description 8
- 238000005859 coupling reaction Methods 0.000 claims abstract description 8
- 239000007789 gas Substances 0.000 claims description 30
- 238000002485 combustion reaction Methods 0.000 claims description 14
- 239000012530 fluid Substances 0.000 claims description 13
- 238000000034 method Methods 0.000 claims description 6
- 230000008569 process Effects 0.000 claims description 6
- 239000002918 waste heat Substances 0.000 claims description 6
- 230000006872 improvement Effects 0.000 claims description 2
- 238000010793 Steam injection (oil industry) Methods 0.000 description 10
- 239000000446 fuel Substances 0.000 description 10
- 238000010586 diagram Methods 0.000 description 5
- 230000001133 acceleration Effects 0.000 description 4
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000010248 power generation Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02C—GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS
- F02C3/00—Gas-turbine plants characterised by the use of combustion products as the working fluid
- F02C3/04—Gas-turbine plants characterised by the use of combustion products as the working fluid having a turbine driving a compressor
- F02C3/10—Gas-turbine plants characterised by the use of combustion products as the working fluid having a turbine driving a compressor with another turbine driving an output shaft but not driving the compressor
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
- F01K21/00—Steam engine plants not otherwise provided for
- F01K21/04—Steam engine plants not otherwise provided for using mixtures of steam and gas; Plants generating or heating steam by bringing water or steam into direct contact with hot gas
- F01K21/047—Steam engine plants not otherwise provided for using mixtures of steam and gas; Plants generating or heating steam by bringing water or steam into direct contact with hot gas having at least one combustion gas turbine
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02C—GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS
- F02C9/00—Controlling gas-turbine plants; Controlling fuel supply in air- breathing jet-propulsion plants
- F02C9/48—Control of fuel supply conjointly with another control of the plant
Abstract
Abstract Steam-Injected Free-Turbine-Type Gas Turbine A steam-injected free-turbine type of gas turbine is disclosed. In order to avoid the necessity of redesigning the compressor/core turbine, the shaft of the core turbine is modified to provide additional load output. As steam is injected into the system the resulting excess power of the core turbine is taken out of the system by coupling the compressor output shaft with a load. Thus, the core turbine operates as a single shaft turbine in addition to the existing power turbine. A control provides control of the load output of the two turbine output shafts so that the compressor/turbine stays in the matched operating domain.
Description
( ~ ~
. ~-`. 12~ 93 , Description Steam-Injected Free-Turbine-T ~ Turbine Technical Field This invention relates to steam injected gas turbine engines of the type having a free or power turbine, and in particular to steam injection into a Cheng cycle engine having a free turbine.
Background Art ; A variety of steam injection gas turbine engine systems exist in the prior art. The high efficiency potential of the Cheng, or Cheng Dual Fluid Cycle engine, as described in U.S. Patent Nos. 4,128,994 and 4,248,039, is realized when a specific amounts of steam is injected into a gas turbine to maximize both the power output and/or the thermal efficiency. The steam is obtained by recovery of the turbine exhaust waste heat. Highest efficiency is obtained at the highest practical steam thermo-dynamic potential. ;
Gas turbines can be divided into two categories;
namely, the single shaft and the so-called free or power turbine versions. A single shaft turbine comprises a compressor, a combustion chamber and a turbine where the com~ressor and the turbine are linked by a mechanical shaft as an integral unit. If minor ; 25 losses are neglected, the excess power, after supplying the compressorls need, becomes the net shaft output.
In such a gas turbine, roughly two-thirds of the turbine power output is consumed in supplying the work requirement of the compressor. The mechanical coupling of the single shaft design resolves the problem of the power split between the output power and the compressor needs. This also resolves the problem of power redistribution due to steam injection into the engine.
( ~ (`
- . 129L3~3 Very often, the single shaft gas turbine is operated at a fixed rpm regardless of the load demand. In this case, fuel flow varies with the turbine inlet temperature and hence, the power output.
In a free turbine type of gas turbine, the compressor is linked to the core or gas generation turbine with a separate turbine section, often called the free or power turbine, to produce power output.
One advantage of this configuration is that it allows the free turbine, which supplies power to the load, to operate at rotational speeds different from the core turbine/compressor/rotor system. In this case, the core turbine provides essentially all the power requirements for the compressor. This requirement forces the compressor/core turbine to be matched in power balance such that the unit must follow a fairly narrow prescribed operating path. This path is defined by the need to match, within certain boundaries, the - compressor and the core turbine performance characteristics. With turbines and compressors as drive and driven components respectively, the match is not maintained at certain rotational speeds, mass flow, and pressure conditions. To have wider matching possibilities variable guide vanes or gas release valves are commonly installed in the compressor, which can temporarily cause a more nearly matched condition under starting and low rotational speed conditionsO
If steam is to be injected into such a turbine -engine, the addition cannot be made arbitrarily. If a free turbine engine is to be retrofitted, for example, to use the Cheng cycle, injecting the total amount of steam produced by the exhaust waste heat into the `~
combustion chamber will result in the power output of the core turbine increasing far beyond what the compressor can absorb at the matched`condition. This is because the power required for the compressor ~Z43~L~3 remains essentially constant and there i8 no convenient way to transf0r the excess core turbine output from the core turbine -to the power or free turbine without a co~plicated mechanical system~ or completely redesigning the core turbine.
Di~closure of tho Invention It is therefore an ob;ect of the invention to provide an improv0d steam injected gas turbine of the free-turbine design Another object of the invention i~ to provide an improved steam-injected Cheng cycle engine of the free-turbine design;
Another object of the invention is to provide steam injection in a free-turbine type of gas turbine or Cheng cycle engine that requires a minimum of design - modification of the core and power turbins section~.
; In accordance with the present invention, a power output 9ha~t is selectively coupled to the corc turbine compressor thereb~ providing a variable output load. Excess power developed by ~the core turbine due to the addition of steam to the engine is, in this manner, used to create useful output power. At the ~ame time it prevents a compressor/core mismatch which would otherwise occur.
Specifically the invention is used in a free turbine type gas turbine comprising: compressor means; a core turbine mechanically coupled with the compressor means mls/LCM
- ' ~2~3~33 - 3a -to power i-t; a power turbine which i8 independent from the core turbine; and a combustion chamber for providing a heated working fluid; means for adding steam to the working fluid; and mean~ for providing a ~ingle flow path for the working fluid, fir~-t through the core turbine and then through the power turbine. The invention relates to the improvement comprising: means for preventing mismatch be-tween the core turbine and the compressor due to the addition of steam comprising coupling a variable output load to the compressor.
The operating characteristics of a free-turbine engine design must be defined in terms of a complicated thermo-dynamic feedback link and the component matching.
Without major -turbine modifications, if steam were injected in large quantities into the combustion chamber of a free turbine type of gas turbine engine, a~ ln the case of~a ~ingle ~haft gas turbine, it would gro~sly up~et its matching conditions.
In accordance with the pre~snt invention the Cheng cycle is incorporated into the free turbine type of engine.
A judicious amount of high enthalpy ~team~
mls/LCM
~ ` lZ~.3'193 {
which can be generated by the waste exhaust heat of a turbine, provides the highest practicable cycle efficiency i~ used in judicious quantities, as defined in Patent No. 4,128,994, but compressor/turbine matching conditions must not be upset and the system must operate within the maximum rpm, surge line and turbine inlet temperature limits. This is accomplished by coupling a load to the compressor.
If an existing free turbine gas turbine system is to be retrofit, for example, to use the Cheng cycle to retain the objectives of high cycle efficiency without major redesign and modification of the basic turbine components, the retrofit cannot be accomplished simply by injecting steam into the combustion cans, as in the case of the single-shaft turbine. The basic difficulty, as already presented above, is attributable to the nature of the core turbine/compressor matching problem. If the steam corresponding to the critical amount required to produce peak e~ficiency in a single shaft Cheng cycle engine is injected into the combustion chamber of an unmodified free turbine engine, both the core turbine and the power turbine will produce increased power. The power output of the core turbine will increase far beyond what the compressor can absorb at the matched condition, since the power required for the compressor remains essentially constant and there is no convenient way to transfer the excess core turbine output from the core turbine to the power output turbine wlthout a complicated mechanical system. The difficulty arises from the fact that the added power output of the core turbine is not needed by the compresso. and cannot be easily transferred to the power output shaft.
1~3~93 Description of the Drawings Figure 1 is a block schematic diagram of a single-shaft gas turbine.
Figure 2 is a block schematic diagram of a free turbine type gas turbine.
Figure 3 is a typical compressor performance map with matched operating path, for the gas turbine of Figure 2.
Figure 4 is a block-diagram representation of a typical control system and its feedback loop for the free turbine engine of Figure 2.
Figure 5 is a performance map which graphically illustrates the typical acceleration and deceleration process of the free turbine engine of Figure 2.
Figure 6 is a schematic block representation of another embo~diment of the present invention utilizing a load coupled to the compressor, in the gas turbine engine of Figure 2.
Figure 7 is a block diagram o~ the control system of the embodiment of Figure 6.
- Figure 8 is a performance map for a typical free turbine with steam injection comparing operations characteristics and regions with and without the present invention.
Detailed Description of the Invention A schematic diagram of a typical single shaft gas turbine 10 is show in Figure 1. It consists of a compressor 12t a combustion chamber 14, and a turbine 16 which is linked rigidly to the compressor and coupled to the load by shaft 18. The turbine need not be matched at the Qperating point with the compressor;
its excess power capability drives the load through the single shaft 18.
A typical free-turbine type of gas turbine 20 is shown in schematic form in Figure 2. The turbine 20 3~3;;~
consists oE a compressor 12', a combustion chamber 14', a core or gas generator turbine 22 which is linked through a mechanical shaEt or rotor 24 to the compressor 12', and a power or free turbine 26 which is connected to the load. The power turbine 26, which has ; no mechanical linkage to the core turbine 22 or compressor 12', is, nonetheless, linked thermodynamically to the engine system as a whole. The core turbine 22 produces essentially all the power required by the compressor 12'.
The power turbine 26 interfaces with the core turbine 22/compressor 12' combination through the mass flow and turbine inlet temperature in a peculiar way.
At increased core turbine inlet temperature, the core turbine 22 produces more power so the compressor 12' is accelerated to a higher rpm, thus delivering more mass flow at a higher pressure ratio. Simultaneously, more mass flow through the power turbine 26 requires higher pressure ratio for its expansion through it. This reduces the pressure ratio of the working fluid across the core turbine 22, thus limiting its power output capability. This aero-thermodynamic feedback is tantamount to a non-mechanical coupling between the core and the power turbines.
The core turbine 22 and the compressor 12' must be matched in design to operate on or near a power-matched opèrating equilibrium path. A core turbine pressure ratio above the e~uilibrium operating path increases the rotational speed of the turbine 22. This higher speed causes the compressor 12' to generate greater pressure ratios. If additional air flow is restricted by the core turbine back pressure, the compressor 12' is forced to operate nearer to its surge region, where, because of flow separation on the compressor vanes, flow becomes unstable. Compressor 12' operation in the surge region is prohibited because of the severe ( (:
3~33 transcient loads imposed on the compressor blades when operating in this region.
Figure 3 is a typical compressor map for free turbine englne 20. The compressor map is represented by a plot of pressure ratio vs. air flow, each parameter corrected by dimensionless variables. The corrected air flow rate is the air flow rate multiplied ; by the square root of 3, the absolute temperature ratio between the ambient temperature and 520 degree R, and divided by the ambient pressure ratio ~, normalized with normal atmospheric pressure at sea-level, 14.7 psia, as a reference point. The other operating parameters are the core turbine/ compressor constant rotational speed lines 32-57.5, again compensated by 15 r~. High pressure ratio low-flow compressor operation is bounded by the compressor surge regionj often called the surge line 82, although the condition where compressor surge occurs is not sufficiently precise to be defined as a line. Constant compressor efEiciency contours are shown by dashed lines 71-77 Compressor map 80 shows two segments of matched core-compressor operating line 86 connected at a certain designed rpm. The lower part 84 o~ the matched line corresponds to operating with an air-bleed valve open so that not all of the air pressurized the compressor 12' is expanded through the core turbine 22.
This air-bleed operation~facilitates startup of the engine and acceleration to its operating speed. The upper segment 87 of the matched line, where the air-bleed valve is closed, beginning at point 88, coversthe power-producing range for the ~ree turbine engine operation. This latter region is usually the region of interest for producin~ engine power. Peak rpm of core turbine 22/compressor 12' occurs at point 89. Turbine rpm is usually referenced to this rpm as 100~ rpm.
' .;
~2~ 3 Figure 4 shows a typical control system 90 for free turbine engine 20. The essential element of the control system 90 is a load level control. Feedback signals 92 from the power turbine 26 are generated by sensing either rpm or torque and sent to the fuel control system 94, which regulates fuel flow 96 for the core turbine 22. Ordinarily, this is all that is - required for a single~shaft gas turbine control. In the free turbine case, however, the two turbine rotational speeds are mechanically independent. This fact requires additional programmed control ~or the uel flow rate. Since the core turbine 22 and the compressor 12' are ma~ched, with a boundary o~
acceleration at the surge region on the compressor map, the control 94 also requires core rotor rpm or torque as a feedback signal 96. Such feedback can also be accomplished by measuring the compressor 12' pressure rise since it is ordinarily related to the rpm directly.
Figure 5 illustrates the typical acceleration and deceleration process of a free turbine engine 20.
Assume that the initial operating point is at IYl on the equilibrium matched path 86, where the core turbine 22 power output matches the compressor 12' power requirement. Addition of more fuel increases the ; temperature of the working fluid, therefore increasing volume flow (and power potential) with the same amount o~ air mass flow. A higher pressure ratio is required to force the fluid, now occupying a larger volume, through the turbine 22. This causes the operating point to move along the constant rpm line 100 to point 1. This point represents a higher turbine output potential than the compressor needs at that rpm. That makes the core turbine rotor 24 accelerate to a new equilibrium position M2 at a higher rpm. This process goes on until the engine core rotor 24 reaches either ~. ( 12~3~3 g the maximum design rpm or the limiting design maximum turbine inlet temperature, at which point some Eorm of control mechanism must limit further increase.
- If point D represents the maximum design rpm point, a deceleration process occurs in a reverse fashion. When fuel is cut back, the temperature of the working fluid decreases. This decreases the volume flow for the same amount of air mass flow. Less pressure ~ratio) is required for the working fluid to pass through the core turbine 22. Due to rotor 24 inertia, the operating point drops off temporarily to point dl along the constant rpm curve 102. This point is below the equilibrium matched operating line 86.
The core turbine 22, therefore, cannot provide the power requirement of the compressor 12'. The operating condition therefore drifts towards a lower rpm operating point d2 on the operating path 86 at a rate that depends on the power deficiency and the inertia of the rotating system.
Figure 6 shows a free turbine 20' in accordance - with the present invention. An output shaft 160 is added to the compressor 12'. A suitable coupling means ; 162, such as a clutch, selectively couples the output shaft 160 of the compressor 12' to a load~ As - 25 explained, when steam is introduced prior to the core turbine 22, such as in the combustion chamber 14', the core turbine 22 produces more power than that required by the compressor 1~'. By coupling a load to the compressor 12', this excess power is turned into useful work output. Additionally, it prevents a mismatch between the compressor 12' and the core turbine 22. As greater amounts of steam are injected within the combustion chamber 14', additional load is coupled to the compressor 12'.
The control system 100 for the free turbine 20' of Figure 6 is illustrated in Figure 7. Control system 1~34~93 --1 o--100 senses the power turbine inlet temperature TIT by means of a suitable thermocouple temperature transmitter 102 which sends signals to the control system 100 via line 104. The load on and torque from free turbine 26 at output 1, along with the power turbine 26 rpm, N2, is sensed by governor 106 and is provided to the control system 100 via feedback line 108. In a similar manner output 2, provided by core turbine 22 through compressor 12' to avoid compressor/core turbine mismatch, is monitored to provide torque/load information via feedback line 110 to control system 100. Core turbine/compressor rpm, Nl, is also provided via line 110 from governor 112.
Control system 100 regulates and controls the fuel flow rate from a suitable fuel source 114 to combustion chamber 14' through a fuel control line 116 which controls a fuel flow valve 118. Control system 100 also controls steam injection from a suitable steam source 120 into combustion chamber 14' through a steam control line 122 which controls a steam flow valve 124.
A suitable steam source can, for example, be a heat exchanger or waste heat boiler such as utilized in Cheng cycle engines as described in ~.S. Patent Nos.
4,128,994 and 4,248,039, assigned to the assignee of the present invention. Also, by utilizing the teachings of these two patents, free turbine engine 20' can be run according to the Cheng cycle. ~
If steam source 120 is a waste heat boiler, steam ~;
control valve 124 advantageously is located between its evaporator and superheater. Such a steam control valve location is described in U.S. Patent 4,393,649, assigned to the assignee of the present invention.
One configuration for control system 100 is described in U.S. Patent Nos. 4,297,841 and 4,417,438, assigned to the assignee of the present invention. In the event that engine 20' is used in the Cheng cycle or ( ~ (`
~2gl3~3 used to produce process steam, this control mode is particularly suitable.
The engine operator provides load demand information for control system 100. Control system 100 provides a load control command signal via line 126 to the output 2 to provide appropriate loading as required to maintain system balance. A variety of load configurations can be used. For example output 2 can comprise a load coupled through a common gear box, including a clutch. If r as another example, engine 20' is used as a powerp]ant for a boat, load management at output 2 can comprise altering the pitch angle of the boat's propeller. The load can be a gas compressor for natural gas, in which case control valves regulate the volume of gas compressed depending upon the load.
Also, regulation of output 2 depending upon the size of the load can comprise regulating the excitation current for the magnetic ~ield of an electrical generator.
In operation, start-up of turbine 20' is the same as for the single shaft turbine 10. As the power turbine rpm, N2, increases, this information is fed back to the control 100 via line 108. The addition of - steam at combustion chamber 14' further increases the power turbine 26 rpm, N2, and compressor rpm Nl. Steam is also judiciously added so as not to exceed the designed rpm limit N1. At the same time additional load is added at output 2, thereby slowing down compressor 12'. This additional load is controlled in such a manner that fuel and steam flow rates are limited to maintain turbine inlet temperatures and the compressor surge margine within design limits~
Assuming power generation from the power turbine 26, engine 20' usually is run at a constant rpm and the power generation limitation is the surge line of the compressor 12'. If the power turbine load, output 2, is a variable rpm one, the control system 100 limits (:` lZ43a~93 both rpm and surge margin of engine 20'. When such a limitation is reached, control system 100 deter~ines the amount of steam flow allowed, so that neither the over-speed limit nor the pressure margin is exceeded.
Figure 8 is a compressor map of a representative free turbine engine, the Allison 501 KF engine. With steam injection, the core turbine rpm, Nl, of engine 20' increases, following the path a-a until the maximum rpm line 128 is reached. In comparison, path c-c is the path for a single shaft engine, such as the Allison 501 KB.
The operating line a-a limitation is overcome when engine 20' is operated in accordance with the present invention. By adding load to the compressor/core turbine when additional steam is injected, engine 20' can follow a constant rpm path b-b, limited only by the surge margin line 130. In fact engine 20' can be operated anywhere in the region bounded by the surge margin line 130, the maximum rpm limit line 128, and line a-a, the matched operating line for a standard steam injected engine.
The following Table I is a comparison of the -~
performance of a steam-injected 501 KF engine, with and without the present invention, in comparison to a 501 - 25 engine without steam injection: ~
, .
Tab.le I
Increased Increased Lbs/Sec Horse~ Efficienc~ o_ Steam 501 KF Standard 5 steam injection 3.5% 18% 3.3 501 KF steam injection using present invention 62% 40% 5.5 . Net Difference 27% 22% 2.2 : ' -,' :
. ~-`. 12~ 93 , Description Steam-Injected Free-Turbine-T ~ Turbine Technical Field This invention relates to steam injected gas turbine engines of the type having a free or power turbine, and in particular to steam injection into a Cheng cycle engine having a free turbine.
Background Art ; A variety of steam injection gas turbine engine systems exist in the prior art. The high efficiency potential of the Cheng, or Cheng Dual Fluid Cycle engine, as described in U.S. Patent Nos. 4,128,994 and 4,248,039, is realized when a specific amounts of steam is injected into a gas turbine to maximize both the power output and/or the thermal efficiency. The steam is obtained by recovery of the turbine exhaust waste heat. Highest efficiency is obtained at the highest practical steam thermo-dynamic potential. ;
Gas turbines can be divided into two categories;
namely, the single shaft and the so-called free or power turbine versions. A single shaft turbine comprises a compressor, a combustion chamber and a turbine where the com~ressor and the turbine are linked by a mechanical shaft as an integral unit. If minor ; 25 losses are neglected, the excess power, after supplying the compressorls need, becomes the net shaft output.
In such a gas turbine, roughly two-thirds of the turbine power output is consumed in supplying the work requirement of the compressor. The mechanical coupling of the single shaft design resolves the problem of the power split between the output power and the compressor needs. This also resolves the problem of power redistribution due to steam injection into the engine.
( ~ (`
- . 129L3~3 Very often, the single shaft gas turbine is operated at a fixed rpm regardless of the load demand. In this case, fuel flow varies with the turbine inlet temperature and hence, the power output.
In a free turbine type of gas turbine, the compressor is linked to the core or gas generation turbine with a separate turbine section, often called the free or power turbine, to produce power output.
One advantage of this configuration is that it allows the free turbine, which supplies power to the load, to operate at rotational speeds different from the core turbine/compressor/rotor system. In this case, the core turbine provides essentially all the power requirements for the compressor. This requirement forces the compressor/core turbine to be matched in power balance such that the unit must follow a fairly narrow prescribed operating path. This path is defined by the need to match, within certain boundaries, the - compressor and the core turbine performance characteristics. With turbines and compressors as drive and driven components respectively, the match is not maintained at certain rotational speeds, mass flow, and pressure conditions. To have wider matching possibilities variable guide vanes or gas release valves are commonly installed in the compressor, which can temporarily cause a more nearly matched condition under starting and low rotational speed conditionsO
If steam is to be injected into such a turbine -engine, the addition cannot be made arbitrarily. If a free turbine engine is to be retrofitted, for example, to use the Cheng cycle, injecting the total amount of steam produced by the exhaust waste heat into the `~
combustion chamber will result in the power output of the core turbine increasing far beyond what the compressor can absorb at the matched`condition. This is because the power required for the compressor ~Z43~L~3 remains essentially constant and there i8 no convenient way to transf0r the excess core turbine output from the core turbine -to the power or free turbine without a co~plicated mechanical system~ or completely redesigning the core turbine.
Di~closure of tho Invention It is therefore an ob;ect of the invention to provide an improv0d steam injected gas turbine of the free-turbine design Another object of the invention i~ to provide an improved steam-injected Cheng cycle engine of the free-turbine design;
Another object of the invention is to provide steam injection in a free-turbine type of gas turbine or Cheng cycle engine that requires a minimum of design - modification of the core and power turbins section~.
; In accordance with the present invention, a power output 9ha~t is selectively coupled to the corc turbine compressor thereb~ providing a variable output load. Excess power developed by ~the core turbine due to the addition of steam to the engine is, in this manner, used to create useful output power. At the ~ame time it prevents a compressor/core mismatch which would otherwise occur.
Specifically the invention is used in a free turbine type gas turbine comprising: compressor means; a core turbine mechanically coupled with the compressor means mls/LCM
- ' ~2~3~33 - 3a -to power i-t; a power turbine which i8 independent from the core turbine; and a combustion chamber for providing a heated working fluid; means for adding steam to the working fluid; and mean~ for providing a ~ingle flow path for the working fluid, fir~-t through the core turbine and then through the power turbine. The invention relates to the improvement comprising: means for preventing mismatch be-tween the core turbine and the compressor due to the addition of steam comprising coupling a variable output load to the compressor.
The operating characteristics of a free-turbine engine design must be defined in terms of a complicated thermo-dynamic feedback link and the component matching.
Without major -turbine modifications, if steam were injected in large quantities into the combustion chamber of a free turbine type of gas turbine engine, a~ ln the case of~a ~ingle ~haft gas turbine, it would gro~sly up~et its matching conditions.
In accordance with the pre~snt invention the Cheng cycle is incorporated into the free turbine type of engine.
A judicious amount of high enthalpy ~team~
mls/LCM
~ ` lZ~.3'193 {
which can be generated by the waste exhaust heat of a turbine, provides the highest practicable cycle efficiency i~ used in judicious quantities, as defined in Patent No. 4,128,994, but compressor/turbine matching conditions must not be upset and the system must operate within the maximum rpm, surge line and turbine inlet temperature limits. This is accomplished by coupling a load to the compressor.
If an existing free turbine gas turbine system is to be retrofit, for example, to use the Cheng cycle to retain the objectives of high cycle efficiency without major redesign and modification of the basic turbine components, the retrofit cannot be accomplished simply by injecting steam into the combustion cans, as in the case of the single-shaft turbine. The basic difficulty, as already presented above, is attributable to the nature of the core turbine/compressor matching problem. If the steam corresponding to the critical amount required to produce peak e~ficiency in a single shaft Cheng cycle engine is injected into the combustion chamber of an unmodified free turbine engine, both the core turbine and the power turbine will produce increased power. The power output of the core turbine will increase far beyond what the compressor can absorb at the matched condition, since the power required for the compressor remains essentially constant and there is no convenient way to transfer the excess core turbine output from the core turbine to the power output turbine wlthout a complicated mechanical system. The difficulty arises from the fact that the added power output of the core turbine is not needed by the compresso. and cannot be easily transferred to the power output shaft.
1~3~93 Description of the Drawings Figure 1 is a block schematic diagram of a single-shaft gas turbine.
Figure 2 is a block schematic diagram of a free turbine type gas turbine.
Figure 3 is a typical compressor performance map with matched operating path, for the gas turbine of Figure 2.
Figure 4 is a block-diagram representation of a typical control system and its feedback loop for the free turbine engine of Figure 2.
Figure 5 is a performance map which graphically illustrates the typical acceleration and deceleration process of the free turbine engine of Figure 2.
Figure 6 is a schematic block representation of another embo~diment of the present invention utilizing a load coupled to the compressor, in the gas turbine engine of Figure 2.
Figure 7 is a block diagram o~ the control system of the embodiment of Figure 6.
- Figure 8 is a performance map for a typical free turbine with steam injection comparing operations characteristics and regions with and without the present invention.
Detailed Description of the Invention A schematic diagram of a typical single shaft gas turbine 10 is show in Figure 1. It consists of a compressor 12t a combustion chamber 14, and a turbine 16 which is linked rigidly to the compressor and coupled to the load by shaft 18. The turbine need not be matched at the Qperating point with the compressor;
its excess power capability drives the load through the single shaft 18.
A typical free-turbine type of gas turbine 20 is shown in schematic form in Figure 2. The turbine 20 3~3;;~
consists oE a compressor 12', a combustion chamber 14', a core or gas generator turbine 22 which is linked through a mechanical shaEt or rotor 24 to the compressor 12', and a power or free turbine 26 which is connected to the load. The power turbine 26, which has ; no mechanical linkage to the core turbine 22 or compressor 12', is, nonetheless, linked thermodynamically to the engine system as a whole. The core turbine 22 produces essentially all the power required by the compressor 12'.
The power turbine 26 interfaces with the core turbine 22/compressor 12' combination through the mass flow and turbine inlet temperature in a peculiar way.
At increased core turbine inlet temperature, the core turbine 22 produces more power so the compressor 12' is accelerated to a higher rpm, thus delivering more mass flow at a higher pressure ratio. Simultaneously, more mass flow through the power turbine 26 requires higher pressure ratio for its expansion through it. This reduces the pressure ratio of the working fluid across the core turbine 22, thus limiting its power output capability. This aero-thermodynamic feedback is tantamount to a non-mechanical coupling between the core and the power turbines.
The core turbine 22 and the compressor 12' must be matched in design to operate on or near a power-matched opèrating equilibrium path. A core turbine pressure ratio above the e~uilibrium operating path increases the rotational speed of the turbine 22. This higher speed causes the compressor 12' to generate greater pressure ratios. If additional air flow is restricted by the core turbine back pressure, the compressor 12' is forced to operate nearer to its surge region, where, because of flow separation on the compressor vanes, flow becomes unstable. Compressor 12' operation in the surge region is prohibited because of the severe ( (:
3~33 transcient loads imposed on the compressor blades when operating in this region.
Figure 3 is a typical compressor map for free turbine englne 20. The compressor map is represented by a plot of pressure ratio vs. air flow, each parameter corrected by dimensionless variables. The corrected air flow rate is the air flow rate multiplied ; by the square root of 3, the absolute temperature ratio between the ambient temperature and 520 degree R, and divided by the ambient pressure ratio ~, normalized with normal atmospheric pressure at sea-level, 14.7 psia, as a reference point. The other operating parameters are the core turbine/ compressor constant rotational speed lines 32-57.5, again compensated by 15 r~. High pressure ratio low-flow compressor operation is bounded by the compressor surge regionj often called the surge line 82, although the condition where compressor surge occurs is not sufficiently precise to be defined as a line. Constant compressor efEiciency contours are shown by dashed lines 71-77 Compressor map 80 shows two segments of matched core-compressor operating line 86 connected at a certain designed rpm. The lower part 84 o~ the matched line corresponds to operating with an air-bleed valve open so that not all of the air pressurized the compressor 12' is expanded through the core turbine 22.
This air-bleed operation~facilitates startup of the engine and acceleration to its operating speed. The upper segment 87 of the matched line, where the air-bleed valve is closed, beginning at point 88, coversthe power-producing range for the ~ree turbine engine operation. This latter region is usually the region of interest for producin~ engine power. Peak rpm of core turbine 22/compressor 12' occurs at point 89. Turbine rpm is usually referenced to this rpm as 100~ rpm.
' .;
~2~ 3 Figure 4 shows a typical control system 90 for free turbine engine 20. The essential element of the control system 90 is a load level control. Feedback signals 92 from the power turbine 26 are generated by sensing either rpm or torque and sent to the fuel control system 94, which regulates fuel flow 96 for the core turbine 22. Ordinarily, this is all that is - required for a single~shaft gas turbine control. In the free turbine case, however, the two turbine rotational speeds are mechanically independent. This fact requires additional programmed control ~or the uel flow rate. Since the core turbine 22 and the compressor 12' are ma~ched, with a boundary o~
acceleration at the surge region on the compressor map, the control 94 also requires core rotor rpm or torque as a feedback signal 96. Such feedback can also be accomplished by measuring the compressor 12' pressure rise since it is ordinarily related to the rpm directly.
Figure 5 illustrates the typical acceleration and deceleration process of a free turbine engine 20.
Assume that the initial operating point is at IYl on the equilibrium matched path 86, where the core turbine 22 power output matches the compressor 12' power requirement. Addition of more fuel increases the ; temperature of the working fluid, therefore increasing volume flow (and power potential) with the same amount o~ air mass flow. A higher pressure ratio is required to force the fluid, now occupying a larger volume, through the turbine 22. This causes the operating point to move along the constant rpm line 100 to point 1. This point represents a higher turbine output potential than the compressor needs at that rpm. That makes the core turbine rotor 24 accelerate to a new equilibrium position M2 at a higher rpm. This process goes on until the engine core rotor 24 reaches either ~. ( 12~3~3 g the maximum design rpm or the limiting design maximum turbine inlet temperature, at which point some Eorm of control mechanism must limit further increase.
- If point D represents the maximum design rpm point, a deceleration process occurs in a reverse fashion. When fuel is cut back, the temperature of the working fluid decreases. This decreases the volume flow for the same amount of air mass flow. Less pressure ~ratio) is required for the working fluid to pass through the core turbine 22. Due to rotor 24 inertia, the operating point drops off temporarily to point dl along the constant rpm curve 102. This point is below the equilibrium matched operating line 86.
The core turbine 22, therefore, cannot provide the power requirement of the compressor 12'. The operating condition therefore drifts towards a lower rpm operating point d2 on the operating path 86 at a rate that depends on the power deficiency and the inertia of the rotating system.
Figure 6 shows a free turbine 20' in accordance - with the present invention. An output shaft 160 is added to the compressor 12'. A suitable coupling means ; 162, such as a clutch, selectively couples the output shaft 160 of the compressor 12' to a load~ As - 25 explained, when steam is introduced prior to the core turbine 22, such as in the combustion chamber 14', the core turbine 22 produces more power than that required by the compressor 1~'. By coupling a load to the compressor 12', this excess power is turned into useful work output. Additionally, it prevents a mismatch between the compressor 12' and the core turbine 22. As greater amounts of steam are injected within the combustion chamber 14', additional load is coupled to the compressor 12'.
The control system 100 for the free turbine 20' of Figure 6 is illustrated in Figure 7. Control system 1~34~93 --1 o--100 senses the power turbine inlet temperature TIT by means of a suitable thermocouple temperature transmitter 102 which sends signals to the control system 100 via line 104. The load on and torque from free turbine 26 at output 1, along with the power turbine 26 rpm, N2, is sensed by governor 106 and is provided to the control system 100 via feedback line 108. In a similar manner output 2, provided by core turbine 22 through compressor 12' to avoid compressor/core turbine mismatch, is monitored to provide torque/load information via feedback line 110 to control system 100. Core turbine/compressor rpm, Nl, is also provided via line 110 from governor 112.
Control system 100 regulates and controls the fuel flow rate from a suitable fuel source 114 to combustion chamber 14' through a fuel control line 116 which controls a fuel flow valve 118. Control system 100 also controls steam injection from a suitable steam source 120 into combustion chamber 14' through a steam control line 122 which controls a steam flow valve 124.
A suitable steam source can, for example, be a heat exchanger or waste heat boiler such as utilized in Cheng cycle engines as described in ~.S. Patent Nos.
4,128,994 and 4,248,039, assigned to the assignee of the present invention. Also, by utilizing the teachings of these two patents, free turbine engine 20' can be run according to the Cheng cycle. ~
If steam source 120 is a waste heat boiler, steam ~;
control valve 124 advantageously is located between its evaporator and superheater. Such a steam control valve location is described in U.S. Patent 4,393,649, assigned to the assignee of the present invention.
One configuration for control system 100 is described in U.S. Patent Nos. 4,297,841 and 4,417,438, assigned to the assignee of the present invention. In the event that engine 20' is used in the Cheng cycle or ( ~ (`
~2gl3~3 used to produce process steam, this control mode is particularly suitable.
The engine operator provides load demand information for control system 100. Control system 100 provides a load control command signal via line 126 to the output 2 to provide appropriate loading as required to maintain system balance. A variety of load configurations can be used. For example output 2 can comprise a load coupled through a common gear box, including a clutch. If r as another example, engine 20' is used as a powerp]ant for a boat, load management at output 2 can comprise altering the pitch angle of the boat's propeller. The load can be a gas compressor for natural gas, in which case control valves regulate the volume of gas compressed depending upon the load.
Also, regulation of output 2 depending upon the size of the load can comprise regulating the excitation current for the magnetic ~ield of an electrical generator.
In operation, start-up of turbine 20' is the same as for the single shaft turbine 10. As the power turbine rpm, N2, increases, this information is fed back to the control 100 via line 108. The addition of - steam at combustion chamber 14' further increases the power turbine 26 rpm, N2, and compressor rpm Nl. Steam is also judiciously added so as not to exceed the designed rpm limit N1. At the same time additional load is added at output 2, thereby slowing down compressor 12'. This additional load is controlled in such a manner that fuel and steam flow rates are limited to maintain turbine inlet temperatures and the compressor surge margine within design limits~
Assuming power generation from the power turbine 26, engine 20' usually is run at a constant rpm and the power generation limitation is the surge line of the compressor 12'. If the power turbine load, output 2, is a variable rpm one, the control system 100 limits (:` lZ43a~93 both rpm and surge margin of engine 20'. When such a limitation is reached, control system 100 deter~ines the amount of steam flow allowed, so that neither the over-speed limit nor the pressure margin is exceeded.
Figure 8 is a compressor map of a representative free turbine engine, the Allison 501 KF engine. With steam injection, the core turbine rpm, Nl, of engine 20' increases, following the path a-a until the maximum rpm line 128 is reached. In comparison, path c-c is the path for a single shaft engine, such as the Allison 501 KB.
The operating line a-a limitation is overcome when engine 20' is operated in accordance with the present invention. By adding load to the compressor/core turbine when additional steam is injected, engine 20' can follow a constant rpm path b-b, limited only by the surge margin line 130. In fact engine 20' can be operated anywhere in the region bounded by the surge margin line 130, the maximum rpm limit line 128, and line a-a, the matched operating line for a standard steam injected engine.
The following Table I is a comparison of the -~
performance of a steam-injected 501 KF engine, with and without the present invention, in comparison to a 501 - 25 engine without steam injection: ~
, .
Tab.le I
Increased Increased Lbs/Sec Horse~ Efficienc~ o_ Steam 501 KF Standard 5 steam injection 3.5% 18% 3.3 501 KF steam injection using present invention 62% 40% 5.5 . Net Difference 27% 22% 2.2 : ' -,' :
Claims (4)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a free turbine type gas turbine comprising:
compressor means;
a core turbine mechanically coupled with said compressor means to power it;
a power turbine which is independent from said core turbine;
and a combustion chamber for providing a heated working fluid;
means for adding steam to said working fluid;
means for providing a single flow path for said working fluid, first through said core turbine and then through said power turbine; and wherein the improvement comprises:
means for preventing mismatch between the core turbine and the compressor due to the addition of steam comprising coupling a variable output load to the compressor.
compressor means;
a core turbine mechanically coupled with said compressor means to power it;
a power turbine which is independent from said core turbine;
and a combustion chamber for providing a heated working fluid;
means for adding steam to said working fluid;
means for providing a single flow path for said working fluid, first through said core turbine and then through said power turbine; and wherein the improvement comprises:
means for preventing mismatch between the core turbine and the compressor due to the addition of steam comprising coupling a variable output load to the compressor.
2. A gas turbine as in claim 1 wherein said steam adding means includes a waste heat boiler for generating steam.
3. A gas turbine as in claim 2 wherein said waste heat boiler additionally provides process steam.
4 . A gas turbine as in claim 1 including means for utilizing the exhausted working fluid gases from said power turbine for steam generation by said steam adding means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/577,899 US4899537A (en) | 1984-02-07 | 1984-02-07 | Steam-injected free-turbine-type gas turbine |
| US577,899 | 1984-02-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1243493A true CA1243493A (en) | 1988-10-25 |
Family
ID=24310586
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000473757A Expired CA1243493A (en) | 1984-02-07 | 1985-02-07 | Steam-injected free-turbine-type gas turbine |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4899537A (en) |
| EP (1) | EP0172224B2 (en) |
| JP (1) | JPS61501104A (en) |
| CA (1) | CA1243493A (en) |
| DE (1) | DE3578095D1 (en) |
| WO (1) | WO1985003550A1 (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5174105A (en) * | 1990-11-09 | 1992-12-29 | General Electric Company | Hot day m & i gas turbine engine and method of operation |
| ES2095474T3 (en) * | 1991-06-17 | 1997-02-16 | Electric Power Res Inst | THERMOELECTRIC POWER PLANT USING COMPRESSED AIR ENERGY ACCUMULATION AND SATURATION. |
| US5201796A (en) * | 1991-10-15 | 1993-04-13 | United Technologies Corporation | Gas turbine engine arrangement |
| US5329758A (en) * | 1993-05-21 | 1994-07-19 | The United States Of America As Represented By The Secretary Of The Navy | Steam-augmented gas turbine |
| US6170264B1 (en) | 1997-09-22 | 2001-01-09 | Clean Energy Systems, Inc. | Hydrocarbon combustion power generation system with CO2 sequestration |
| DE19902437C5 (en) * | 1999-01-22 | 2017-01-12 | General Electric Technology Gmbh | Method and device for rapid startup and for rapid increase in output of a gas turbine plant |
| US6212871B1 (en) * | 1999-03-11 | 2001-04-10 | Alm Development, Inc. | Method of operation of a gas turbine engine and a gas turbine engine |
| US6202782B1 (en) * | 1999-05-03 | 2001-03-20 | Takefumi Hatanaka | Vehicle driving method and hybrid vehicle propulsion system |
| US6247316B1 (en) | 2000-03-22 | 2001-06-19 | Clean Energy Systems, Inc. | Clean air engines for transportation and other power applications |
| AU2001276823A1 (en) * | 2000-05-12 | 2001-12-03 | Clean Energy Systems, Inc. | Semi-closed brayton cycle gas turbine power systems |
| WO2003049122A2 (en) * | 2001-12-03 | 2003-06-12 | Clean Energy Systems, Inc. | Coal and syngas fueled power generation systems featuring zero atmospheric emissions |
| US6945029B2 (en) * | 2002-11-15 | 2005-09-20 | Clean Energy Systems, Inc. | Low pollution power generation system with ion transfer membrane air separation |
| WO2004081479A2 (en) * | 2003-03-10 | 2004-09-23 | Clean Energy Systems, Inc. | Reheat heat exchanger power generation systems |
| US20050241311A1 (en) | 2004-04-16 | 2005-11-03 | Pronske Keith L | Zero emissions closed rankine cycle power system |
| US20100005775A1 (en) * | 2008-05-28 | 2010-01-14 | John Kipping | Combined cycle powered railway locomotive |
| US8164208B2 (en) * | 2009-04-15 | 2012-04-24 | General Electric Company | Systems involving multi-spool generators and variable speed electrical generators |
| MX2012003097A (en) | 2009-09-13 | 2012-08-03 | Lean Flame Inc | Method of fuel staging in combustion apparatus. |
| US10041407B2 (en) | 2011-03-29 | 2018-08-07 | General Electric Company | System and method for air extraction from gas turbine engines |
| JP6222993B2 (en) * | 2013-05-28 | 2017-11-01 | 三菱日立パワーシステムズ株式会社 | 2-shaft gas turbine |
| PL3075982T3 (en) * | 2013-11-27 | 2020-05-18 | Hitachi, Ltd. | Gas turbine suitable for renewable energy and control method thereof |
| EP2952694A1 (en) * | 2014-06-06 | 2015-12-09 | Siemens Aktiengesellschaft | Method for managing a gas turbine assembly at low speed and corresponding gas turbine assembly |
| JP6607772B2 (en) * | 2015-12-03 | 2019-11-20 | 三菱日立パワーシステムズ株式会社 | Two-shaft gas turbine having a steam injection mechanism |
| CN114060102B (en) * | 2021-11-10 | 2022-11-04 | 北京航空航天大学 | Method and device for determining outlet metal angle of guide vane blade |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH323116A (en) * | 1953-03-05 | 1957-07-15 | Siemens Ag | Gas turbine plant with separate machine sets for generating the compressor power and the useful power |
| CH394716A (en) * | 1961-12-19 | 1965-06-30 | Sulzer Ag | Steam generating plant with a gas turbine plant |
| GB1102591A (en) * | 1964-05-22 | 1968-02-07 | Auto Transmissions Ltd | Power transmission system for a gas turbine engine |
| US3359723A (en) * | 1965-10-29 | 1967-12-26 | Exxon Research Engineering Co | Method of combusting a residual fuel utilizing a two-stage air injection technique and an intermediate steam injection step |
| US3521448A (en) * | 1968-09-23 | 1970-07-21 | United Aircraft Corp | Remotely controlled rotary input signal means for introducing trim control signal corrections to jet engine fuel controls |
| US3693347A (en) * | 1971-05-12 | 1972-09-26 | Gen Electric | Steam injection in gas turbines having fixed geometry components |
| DE2655868A1 (en) * | 1976-12-09 | 1978-06-15 | Motoren Turbinen Union | Gas turbine engine for motor vehicles - has connection between power take off and take off drive through adjustable torque converter |
-
1984
- 1984-02-07 US US06/577,899 patent/US4899537A/en not_active Expired - Lifetime
-
1985
- 1985-01-30 WO PCT/US1985/000158 patent/WO1985003550A1/en active IP Right Grant
- 1985-01-30 EP EP85901170A patent/EP0172224B2/en not_active Expired - Lifetime
- 1985-01-30 JP JP60500936A patent/JPS61501104A/en active Granted
- 1985-01-30 DE DE8585901170T patent/DE3578095D1/en not_active Expired - Lifetime
- 1985-02-07 CA CA000473757A patent/CA1243493A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0172224A4 (en) | 1986-07-30 |
| WO1985003550A1 (en) | 1985-08-15 |
| JPS61501104A (en) | 1986-05-29 |
| EP0172224B2 (en) | 1995-11-08 |
| JPH0585734B2 (en) | 1993-12-08 |
| EP0172224B1 (en) | 1990-06-06 |
| US4899537A (en) | 1990-02-13 |
| EP0172224A1 (en) | 1986-02-26 |
| DE3578095D1 (en) | 1990-07-12 |
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